1. Field of the Invention
The present invention relates to power control of a spread spectrum communication system, and more particularly, to a reverse power control device and method for reducing interference between terminals, in which a base station controls transmission power of terminals.
2. Description of the Related Art
In a spread spectrum communication system, a base station compares transmission power of terminals with a threshold value, to command the terminals to reduce the transmission power if it is greater than the threshold value and otherwise command the terminals to increase the transmission power, so as to receive a signal with a desired strength. The reduction in the transmission power of one terminal leads to a reduction in interference with the other terminals.
Power control operation of a conventional CDMA (Code Division Multiple Access) communication system will be described hereinbelow. First, as to the reception operation of the base station, demodulators demodulate RF (Radio Frequency) signals received from the terminals. The demodulators may be composed of an RF demodulator for frequency shifting the received RF signal into the baseband signal and a baseband demodulator for demodulating the baseband signal into the original signal by despreading it. Signal power measurement parts measure the signal quality such as a received signal strength indicator (RSSI), a signal-to-interference ratio (SIR) and a bit error rate (BER) by analyzing the power of the signals output from the demodulators. Power control bit (PCB) generators generate power control bits according to the power measurement results.
Next, as to the transmission operation of the base station, PCB multiplexers multiplex the power control bits to the transmission signals output from baseband signal processors. RF modulators modulate the transmission signals with the power control bits output from the PCB multiplexers into the RF signals. A summer sums the transmission signals output from the RF modulators, and an RF signal processor converts the transmission signal output from the summer into the RF transmission signal.
However, an increase in the transmission power of one terminal by the above base station causes the increase in interference with the terminals, thus resulting in the deterioration of the signals. To compensate for the signal deterioration, the terminals need to increase the transmission power, which may cause vicious circle of the signal deterioration.